Temperature-indicating instrumentality



Jan. 6, 1942. PERRY TEMPERATURE-INDICATING INSTRUMENTALITY Filed July 26, 1940 I Ina/24202": 7 Lloyd Mlerry, I 2396.

Patented Jan. 6, 1942 TEMPERATURE-INDICATE G INSTBUMENTALITY Lloyd M. Perry, Nashua, N. 11., assignor to Nashua Gummed and Coated Paper Company, Nashua, N. IL, a corporation of Massachusetts Application July as, 1940, Serial No. 347,463

13 Claims.

The object of this invention is to provide an instrumentality permitting the expeditious and inexpensive determination of whether a heated appliance has a desired minimum temperature at some selected portion thereof. The instrumentality may be in the form'of a thin sheet or strip which when brought into momentary contact with the appliance will, if the latter at the point of application is at the critical temperature, undergo a change, preferably irreversible in its nature, indicating the fact. Many appliances used in the face of the ironelement without local cold spots I Likewise there should be a uniform pressure between the cooperating parts, such as the support arts utilize a heated platen, roll or like pressure element cooperating with a counter-pressure element. Such embodiment of my invention as is about to be described is one which is particularly adapted to test such' appliances as it may be introduced into or fed through the bite of such a pressure couple and will serve to give an indication of whether the parts are in proper mutual relation at such bite in the locality of the. test, and if so, whether locally of proper temperature. As a large field for application of the invention is found in connection with laundry ironing machinery, for the sake of the convenience of a specific description but by way of example only and without limitation thereto except as the context otherwise indicates, the following description is specifically of its application to the testing of such machinery, and for the same reasons examples-of such machinery are illustrated in the accompanying drawing which is referred to in the following description and wherein:

Fig. 1 is a fragmentary-perspective view of a fiat-work ironer about to be tested to determine the proper operating and the iron in Fig. '2, or between the rolls 6 and the chest 8 against which it works in Fig. l, without local excessive clearances, since in such cases, even although the actual temperature of the heated element at that point might be correct, the work would not be treated in the same manner as in those locations where the pressure is correct.

In accordance with the invention indicating means is provided in the form of a film-like sheet or strip of slight thickness, so cheap as to be expendible for a single use, and which may be placed in or fed through the bite of the cooperating parts and which at the critical temperature will be subject to a sharply defined change in appearance when and if in firm heat-conducting relation to theseparts, as will be the case when they are at optimum operative contact, the film because of its thin sheet-like character permitting its introduction into the close bite of the mechanically opposed parts without difliculty.

es Referring now to Fig. 3, there may be utilized a inthe form of steam chests. The work is fedbetween the roll and the steamchests. In Fig. 2

there is shown a garment press comprising a padded base In over which the garment to be pressed is spread anda swinging heated pressure element optimum temperature for operation of such ironing machines is 330 n, and this temperature thin film-like base ll conveniently of paper having a colored surface in the sensethat it is of such color over all or a part of its area as to contrast sharply in hue and shade with the coating or'obscuring stratum hereinafter referred to. In the annexed claims for the sake of clearness and to distinguish from the coating film I have referred to this base as paper," using the word in an exemplary sense. This base is covered by an obscuring film I. comprising a finely divided solid substance which will melt sharply at the desired temperature and which is preferably dispersed in a binding material as illustrated diagrammatically in Fig. 3 of the drawing by a stippling of the layer It although preferably not entirely immersed in such binding material, as hereinafter more fully explained. The general principle of operation is that the finely divided solid substance obscures, and preferably completely hides,- the colored surface of the paper immediately beneath the same, but on being sub- .iect momentarily to the critical temperature of the solid material melts and becomes sufliciently translucent to disclose the contrasting color of t P per base hitherto obscured. Thus, by way of example, for the particular requirements of laundry machines the following materials and organization are suitable. 'I'he'base may be a P per, conveniently of the coated type, of a dark should be uniform throughout the operative surtil-blue color on one side to which the obscuring stratum it has been applied as in initially fluid, coatable material obtained by grinding dextromannitol (CsHuOc) with a solution of polystyrene resin in propylene dichloride. The resulting coating compound may be spread upon the paper. base II and on evaporation of the propylene di- -chloride a layer is deposited which is adherent to the paper and which comprises the finely divided mannitol distributed throughout the body of the resin binder and preferably exposed at the face of the coating layer, the whole forming a substantially opaque coating effectively obscuring the colored face of the paper It beneath. To illustrate further by a specific example, a mixture of approximately twenty-eight parts of the binder to seventy-two parts of the mannitol by their use, and I recommend coatings of less than two mils in thickness.

Such a product P as illustrated in Fig. 3 may Mannitol, as above referred to, is very suitable for laundry work. It melts at the desired temperature. It will be noted further that it is nonvolatile, non-toxic, inodorous, colorless and water-soluble. If any part of the material is transferred to the appliance and hence to the clothes, there will either be no noticeable stain or one readi y removed-by ordinary washing methods;

clean after the test although the coating as a conveniently be supplied in the form of a tape.

A characteristic method of use is illustrated in Figs. 1 and 2. In Fig. 1 we may assume that the roll 6 is stopped and strips of the tape-like product P of sufficient length may be inserted at various points along the length of the roll, usually at the middle and adjacent either end, with the coated face outward so that when the roll is turned over, the strips will be carried around with the coated surface presented to the heated chest against which the roll works. The ends of the strips may be tucked into the usual cover flaps in order to cause them to move with the roll. The mannitol melts sharply at about 328 F., substantially the desired operating temperature of the mechanism, whereas the resin binder will be substantially unaffected by such temperature. (My observations set the melting point at 328 F.; some authorities, however, state it to be 166 C.) Therefore, if the surface temperature of the heated chest is high enough, such melting takes place at those locations where adequate contact is had between the parts, and the layer it at that point, while persisting as such on the face of the paper base It, becomes translucent in the manner hereinafter more fully explained, per: mitting the dark colored face of the paper to be viewed therethrough. Thus by asingle pass of the test paper P through the bite of the cooperating elements it is disclosed whether the heating element is as hot as desiredand whether proper contact is made between the parts at the location where the test is made. Uusually it is sufllcient to make a test as shown mm. 1, as u the results are positive adjacent the ends of the whole is not softened at the temperature involved to such a degree as to become sticky and itself to "offset to the iron or to be separated from the paper base I! on which it is mounted.

The choice of materials exemplified by the specific example given results from the application of certain principles hereinafter more fully discussed. The fundamental requirement is a meltable substance which will melt sharply at the required temperature, conveniently and preferably a single chemical compound. Such a substance ordinarily would be sought among crystals for crystalline purity would ordinarily be necessaryto insure adequate sharpness of nielt ing point. Such crystals, however, as are obtained from solution by ordinary methods are not generally useful as such. In other words, a crystalline material having the requisite melting point wouldnot in the form as produced from a solution by ordinary methods and in which it ordinarily would be procuredfrom a dealer in chemical suppliesbe usable assuch. We are roll and at a middle point, the contact may beconsidered as adequate throughout the length of the bite.

. Referring to Fig. 2, the method there is substantially similar. 'Ihree strips of the tape' P are stretched upon the padded support ll along not concerned with piling up a thick layer of granular material say an eighth of an inch or more deep, but on the contrary with producing an obscuring film not more than a few thousandths of an inch thick. Crystals of substantial size have relatively low capacity, and, although .in a popular sense small, have a relatively low peripheral surface relative to their volume. Be-

ing 'in themselvesof relatively low opacity andof poor. light-reflecting power, they therefore would have poor hiding or obscuring qualities in thezthin layer which it is commercially practicable and desirable to use. To increase the surface area available and render a minimum coating of the crystals as opaque as possible, resort may be had to a fine'grinding so that the transition from the solid and opaque form to the fluid and therefore translucent form maybe sharply visible. In other words, while the' material is crystalline, it is not utilized in the form of ordinary commercial crystals but is suitably trlturated. 'This desired fine comminutio'n of the material I shall hereinafter express by referring to it as impalpable, which in the usual case will also be lexicographically correct as the resultant particles would not be gritty to the touch.

Crystalsaremostreadilyreducedtothisfine.

state if ground in a rather viscous medium such asthevehiclebywhich theyare securedtothe paper base. Reverting to a specific example, the grinding of such a crystal as mannitol should be such thatsubstantially' none of the resulting particles exceed three mils in diameter and the 'maiorportionsarelessthantwomils. Ingenthe length thereof conveniently at the middle and at either side with the coated surface upward and the iron I! is momentarily lowered.

The result of the test will definitely dei'lerrniitle whether the temperature is suillciently high and whether the adjustment of the padding is correct for emcient use.

"eral increased fineness promotes ease of application,increaseshidingpowerandpemitsthe thickness of the coating to beminimized as is hignlydesirable. Inthecaseofthesixpounds per ream coating above referred to, much the greater portion-of the particles should exceed but little one-half mil in diameter.

'dissolved binding material as hereinafter referred to, is in any 'event preferably dispersed in an appropriate solution of the binder to form a composition which may be applied to the paper in the manner of a paint and wherein the ground crystal corresponds to the pigment and wherein a binder is present which holds the particles after the "paint has dried" and a vehicle or solvent for the binder to render the material fluent and capable of being spread on the paper backing as a coating. The proportions of the binder and crystal are preferably such that in the dried coating the solid material is not completely immersed and this is particularly imlayer of'meltable solid involved but a more prolonged exposure is not, however, excluded. The change in form is essentially irreversible, and after the m terial has once melted it does not return to e state in which it functions as an obscuring layer, at least within such ordinary limitations of time as would be of significance in practical use.

Reference is made in the preceding description to certain materials and their melting points in degrees Fahrenheit are given. With these mate- I rials in practically available states of purity a portant if the refractive index of the solid maemersed at the surface presenting a multiplicity of light-reflecting surfaces with resultant obscuring of thecolor of the paper base.

Such coatings as described when applied to the paper base and solidified give a uniform obscuring film which when viewed with the naked eye (megascopically) appears homogeneous.

In selecting the binder and the vehicle above referred to, neitherthe binder nor the solvent therefor should dissolve or chemically react with the solid material or modify the melting characteristics thereof. Thus, notably, in the case of a water-soluble crystal the vehicle should not be an aqueous one. It is desirable that the binder as deposited from the solution should have refractive properties substantially different from those of the solid material to enhance the opaque character of the obscuring layer although this is of less importance if, as recommended above,.

the solid material is in part emersed from the final coating. The binder shouldbe resistant to the temperature involved. Thus in the example given the'polystyrene resin does not markedly minimum temperature.

soften or become objectionably sticky at temperatures well over 330 F. so that there is little danger of its being lifted from the paper base and adhering to the iron. Propylene dichloride,

the solvent utilized, while adapted to the par-,

ticular example given, is of quite extended utility .as it is readily evaporated and is chemically inert .to or a non-solvent of a considerable number of crystal materials in contrast, for example, to ethyl alcohol or water.

Obviously it is impossible to catalog materials which could be used, either asthe solid meltable constituent, the binder therefor or the solvent for the latter, as the choice will vary in accord-' simple chemical compounds which might be used as the crystal component I may instance adipic acid .(CGHIOOO melting at 300 F.-, gallic 'acid (CwHOs) melting at 450 F., and phenolphthalein (010111404) melting at 495 F. It is obvious, furthermore, that certain materials would be operative but would be of little utility practically because there would be no particular commercial demand for the test of a mechanism at the temperature corresponding to their'melting points.

It will be noted that the test given is of a minimum temperature. It is effective on a short exposure to heat because of the thinness of the ature (the eutectic point) in the same manner close approach to such a temperature is commerci'ally attainable and preferably for ordinary uses there should be a sharp change between a substantially obscured color to a fully disclosed color within a relatively small temperature range, say about 5 F., although a more. gradually manifested change in color might in some instances be desirable for certain users.

The device as described operates only on a If it is desired to observe also whether a maximum temperature is exceeded, test papers embodying substances melting at different but neighboring temperatures may be employed, and when, the one operating at the lower temperature changes color but the other does not, the temperature of the appliance will be between the two, that is, the observation will be like that of the "go and no go" points of a linear dimension gauge.

'While a simple chemical compound is to be preferred, if no compound of the proper characterlstics is readily available, satisfactory results may be obtained by a mixture of pure compounds, and for simplicity reference will be made to a two. component mixture, that is, a mixture of two compounds. In general if two crystalline materials are mixed, all or a portion of the mixture will pass into a fluid stage at some temperature diflerent from the melting point of either pure. crystal alone, and in many instances this temperature will be lower than the melting points of either of the pure crystals. There is therefore.

the possibility of obtaining a desired point and range of thermal response-by varying the .ingredients, and their proportions, opening a field of 'speciflc invention only partially explored. Broadly the following aspects may be pointed out.

Certain solid substances, when mixed in definite proportions, form a eutectic mixture wherein the two'will melt at a definite minimum temperas a simple substance, and this melting point will usually bediflerent from the melting point of either substance alone. Suitable crystals in proportions forming such a eutectic mixture would be utilizable as the solid meltablecon stituent in carrying out the invention to provide an indication of a minimum'temperature corresponding to such eutectic point. 1

In other cases, when the two substances form a solid solution, the mixture when heated to a certain minimum temperature will commence to 'pass into the liquid phase, the liquid phase having a different percentage composition from the remaining solid phase. If the percentage proportions are plotted against temperature, the well known solidus and liquidus curves reault and the distance on the temperature axis "-for any given composition represents the melting point range'of the mixture. In some cases there is a region in which these curves approach concur- Qrency within a small range of temperature. Therefore, a mixture of such substances within particular proportions would correspond to a at a desired temperature.

As an example of a two-component crystalline mixture useful for the'purposes of the invention I may instance a mixture of 33% of mannitol with 67% of sucrose. The melting point of the former is about 328 F. and of the latter about 366 F. The mixture, prepared and used as herein described, gives a usefully sharp indication point of 304 F. I believe that this mixture is an example of a eutectic mixture since the melting point thereof appears to be as sharp as that of either of the components, whereas other mixtures of these components which will also melt at about 304 F. have a much broader threshold of incipient melting. However, the empirical result is as stated'whatever the accurate description of the physical facts involved, and such a mixture is useful to provide an indication at the temperature given. Another example of a useful twocomponent mixture is 70% adipic acid, which itself melts at approximately 300 F., and mannitol, the mixture giving a'practically sharp indicationat 286 F.

These examples indicate the adaptability of mixed crystals to indicate a temperature whereat no suitable single crystal would function,,and show the possibility of providing a series of indicating papers covering a considerable range of temperatures byv rather narrow steps.

It might be added that the solid material used, besides being sharply meltable and, when applied as described insoluble in and non-reactive with the vehicle, should be of good permanence and not affected by atmospheric conditions. For instance, the material, and particularly water-soluble material, should not be deliquescent, by which humidity is high, it must be non-hygroscopic to the extent that its non-melting point is not afrected by reasonably prolonged exposure to atmospheres of eighty percent relative humidity as the opaque character of the tat paper might then be impaired'or lost prior to use. The statement that the solid material should be insoluble in the solid binder or'itsvehicle signifies, of course, that it is not soluble in these materials possible resultant product is to be contrasted with one embodying the thin, mechanically stable film of high obscuring capacity contemplated by my invention. I am also aware that it has been proposed to utilize a bulky mass of meltable material superposed on some indicator and designed either to melt and run away or, if retained in position, by its alternating fusion and solidification either to permit the inspection of such an indicator or to hide it by an interposed solid mass. Sympathetic inks'of which the ingredients undergo a chemical change with a change of color at a more or less definite temperature are well known.

I am aware that the invention may be embodied in other specific forms without departing ature comprising a paper base having acolored face covered by a film of a color different from the base and normally obscuring the latter, which film comprises an adhesive binder non-fusible at the said minimum temperature which retains distributed therethroug'h a light-intercepting assemblage of impalpable particles of a substance which melts at the said minimum temperature thereby causing it to become transpicuous to reveal the color of the underlying base.

2. An instrumentality for determining whether I an appliance has an effective minimum temperature comprising a paper base having a colored face covered by an obscuring film consisting of a matrix of binding material having distributed therethrough fine solid particles of a substance of sharply defined melting point corresponding to said minimum temperature, the binding material being substantially inert with respect to said substance and substantially permanent at the melting point thereof, the substance and the binder being of substantially different light-refracting capacity, a film becoming transpicuous to reveal the color of the base when the instrwmentality is briefly exposed to such minimum temperature.

3. An instrumentality for determining whether an appliance has an effective minimum temperature comprising a paper base having a colored face covered by a megascopically homogenous obscuring film consisting of an adhesive binder at any temperature below the normal temperatures of mixing or below the melting Point of the crystal. It is immaterial if the material when I am aware that it has been proposed to provide an indicating instrumentality by causing a heat-sensitive material to crystallize out from a solution on a can'ier'element. Sucha proceeding is most favorable to the origin and growth of largecrystal masses-in sparse distribution and the retaining in substantially uniform dispersion over said face finely divided solid particles of a substance of a sharply defined melting point corresponding to said minimum temperature, the particles being partially emersed from said adhesive to provide a multiplicity of refractive surfaces, the binding material being substantially inert with respect to said substance and substantially permanent at themelting point thereof, the film becoming transpicuous to reveal the color of the base when the instrumentality is briefly exposed to such minimum temperature.

4. An instrumentality for determining whether an appliance has an effective minimum temperature comprising a paper base having a colored face covered by a megascopically homogeneous obscuring film consisting of an adhesive binder retaining in substantially uniform dispersion over said face an impalpably subdivided substance of terials of said appliance and to the work treated sharply defined melting point corresponding to said minimum temperature, the binding material being substantially inert with respect to said substance and substantially'permanent at the melting point thereof, the film becoming transpicuous to reveal the color of the base when the instrumentality is briefly exposed to such minimum temperature.

5. An instrumentality for determining whether an appliance has an effective minimum temperature comprising a paper base having a colored face covered by an obscuring film not greater than three mils in thickness comprising an inert adhesive binder which retains therein an effectively light-intercepting stratum of crystalline material which melts'at the desired temperature to become transpicuous whereby to reveal they 7 color of the base, such material being present in the form of discrete particles, substantially none of which exceed three mils in mean diameter and the major portion of which is less than two mils in mean diameter.

6. An instrumentality for determining whether 'an appliance has an effective minimum temperature comprising apaper base having a colored face covered by an obscuring film consisting of an inert adhesive binder retaining in substantially uniform dispersion a mixtureof crystalline materials which within a temperature. range closely approximating such minimum temperature will melt substantially as one to cause the film to become transpicuous to reveal the color of the 'base.

'7. An instrumentality for determining whether an'appliance has an effective minimum temperature comprising a paper base having a colored face covered by an obscuring film consisting of an inert adhesive binder retaining insubstantially uniform dispersion a eutectic mixture of crystalline materials which will melt at the desired temperature to cause the film to become transpicuous to reveal the color of the base.

thereby and having a melting point corresponding substantially to the desired minimum temperature of the appliance, which particles are secured to said face in collocation to provide an F., collocated to provide an obscuring film over said face which film on the melting of said substance becomes transpicuous to reveal the color of the base.

11. A-thermosensitive testing instrumentality for use in determining whether an appliance has attained a minimum temperature of substantially 304 F. comprising a paper base having a colored face over which is secured an intimate mixture of generally discrete particles of finely powdered sucrose and mannitol in the proportions of about two parts of the former to one of the latter and collocated to provide an obscuring film over said face which film on the melting of said substance becomes transpicuous to reveal the color of the baSe. I I

12. A, thermosensitive testing in'strumntality for. determining whether an appliance has an effective minimum temperature comprising a paper base having a colored face normally obscured by a multiplicity of finely divided par- 8. A coatable composition for heat testing comprising a suspension of a finely divided, sharply melting, non-deliquescentsubstance in a solution of binding material, both'the binding material and its solvent being chemically inert to said substance and incapable of substantially dissolving the same, the composition when applied as a coating forming on evaporation of the solvent a film megascopically homogeneous and substantially opaque and wherein the binding material is substantially permanent at the melt ing point of the substance.

9. A thermosensitive testing instrumentality for heated laundry appliances comprising a paper substantially to the desired operating tempera ticles adhering thereto and-collocated as a substantially continuous film thereover, said particles consisting of-an intimate mixture of crystalline materials which within a temperature range closely approximating su'ch minimum temperature will melt substantially as one to cause the film to-become transpicuous to reveal the color of the base.

13. The method of determining coinstantaneously the operative conditions of the elements ofa heated couple which are pressed closely together to receive the work between them which comprises causing the couple to close ,on a thin, freely flexible pellicle havingan at least partly colored surface covered by an obscuring film which'at a critical temperature corresponding ture becomes transparent to reveal said surface whereby local changes are effected-indicative of 1 the degree of local opposition of the surfaces and base having a colored face, discrete particles of a non-volatile, non-deliquescent, water-soluble, substantially colorless powder inert to the ina the effective temperature of the properly opposed LLOYD H. PERRY. 

